﻿//===================================================================================
// Microsoft Developer & Platform Evangelism
//=================================================================================== 
// THIS CODE AND INFORMATION ARE PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND, 
// EITHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE IMPLIED WARRANTIES 
// OF MERCHANTABILITY AND/OR FITNESS FOR A PARTICULAR PURPOSE.
//===================================================================================
// Copyright (c) Microsoft Corporation.  All Rights Reserved.
// This code is released under the terms of the MS-LPL license, 
// http://microsoftnlayerapp.codeplex.com/license
//===================================================================================
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;


namespace ESF.MUP.BasePlatform.Infrastructure.Model
{

    internal static class IdentityGenerator
    {
        
        /// <summary>
        /// This algorithm generates secuential GUIDs across system boundaries, ideal for databases 
        /// </summary>
        /// <returns></returns>
        public static Guid NewSequentialGuid()
        {
            byte[] uid = Guid.NewGuid().ToByteArray();
            byte[] binDate = BitConverter.GetBytes(DateTime.UtcNow.Ticks);

            byte[] secuentialGuid = new byte[uid.Length];
             
            secuentialGuid[0] = uid[0];
            secuentialGuid[1] = uid[1];
            secuentialGuid[2] = uid[2];
            secuentialGuid[3] = uid[3];
            secuentialGuid[4] = uid[4];
            secuentialGuid[5] = uid[5];
            secuentialGuid[6] = uid[6];
            // set the first part of the 8th byte to '1100' so     
            // later we'll be able to validate it was generated by us   

            secuentialGuid[7] = (byte)(0xc0 | (0xf & uid[7]));

            // the last 8 bytes are sequential,    
            // it minimizes index fragmentation   
            // to a degree as long as there are not a large    
            // number of Secuential-Guids generated per millisecond  

            secuentialGuid[9] = binDate[0];
            secuentialGuid[8] = binDate[1];
            secuentialGuid[15] = binDate[2];
            secuentialGuid[14] = binDate[3];
            secuentialGuid[13] = binDate[4];
            secuentialGuid[12] = binDate[5];
            secuentialGuid[11] = binDate[6];
            secuentialGuid[10] = binDate[7];

            return new Guid(secuentialGuid);
        }
    }
}
